PostgreSQL提供程序向Entity Framework for Contains和Concat生成的查询错误

Question

I'm using EF to connect to PostgreSQL. EF is in 5.0 version, Npgsql in 2.0.14.3.

The query that I want to run is:

var list = new List<string> { "test" };

var res = from t in db.Test
    where !list.Contains(string.Concat(t.test1, "_", t.test2))
    select t;
res.ToList();

The query that is generated is something like:

SELECT "Extent1"."id" AS "id","Extent1"."test1" AS "test1","Extent1"."test2" AS "test2" FROM "public"."test" AS "Extent1" WHERE 'test'!="Extent1"."test1" || '_' || "Extent1"."test2"

And when I run it I get an error: argument of WHERE must be type boolean, not type text .

However, when I change != to = it works. It works also when I add a parantheses around concatenated strings in Postgres but I cannot change the query that EF generates.

The workaround is that I add the second (dummy) element to the list because then EF generates a bit different query but it isn't an elegant solution…

Is it a bug in pgSQL? Or maybe in EF provider? Can you suggest a better solution to that problem?

MORE INFORMATION

The table script:

CREATE TABLE test
(
  test1 character varying(255),
  test2 character varying(255),
  id integer NOT NULL,
  CONSTRAINT "PK" PRIMARY KEY (id)
)
WITH (
  OIDS=FALSE
);

The class for the table:

[Table("test", Schema = "public")]
public class Test
{
    [Key]
    public int id { get; set; }

    public string test1 { get; set; }

    public string test2 { get; set; }
}

App.config:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=4.4.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
  </configSections>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework" />
  </entityFramework>
  <connectionStrings>
    <add name="local" connectionString="Server=localhost;Port=5432;Database=test;User Id=user;Password=password;" providerName="Npgsql" />
  </connectionStrings>
  <system.data>
    <DbProviderFactories>
      <add name="Npgsql Data Provider" invariant="Npgsql" description="Data Provider for PostgreSQL" type="Npgsql.NpgsqlFactory, Npgsql" />
    </DbProviderFactories>
  </system.data>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0" />
  </startup>
</configuration>

Answer 1

Yes, that's a bug in the EF provider Npgsql.

According to http://www.postgresql.org/docs/9.3/static/sql-syntax-lexical.html#SQL-PRECEDENCE-TABLE , != and || are among (any other) , which means they have the same precedence. They are also left associative, so that query will be parsed as

SELECT ... FROM "public"."test" AS "Extent1"
WHERE ((('test'!="Extent1"."test1") || '_') || "Extent1"."test2")

which is wrong. The correct parsing would be

SELECT ... FROM "public"."test" AS "Extent1"
WHERE ('test'!=(("Extent1"."test1" || '_') || "Extent1"."test2"))

= have lower precedence than != so that works.

A fix for this is included in the pull request at https://github.com/npgsql/Npgsql/pull/256 .